The covers and cases noted above are usually made of resins, and they have upright projections with central axial holes formed as part fitting holes. Metal female screws or like parts are pressure fitted and secured in position in such part fitting holes. Heretofore, such metal female screws were pressure fitted and secured in position in part fitting holes either manually or by using a machine.
In the prior art manual method of pressure fitting, metal parts a (FIGS. 14A) are set one by one in a predetermined orientation on a metallic parts array support, thus forming their lattice-like array thereon, and then they are heated to 200 to 500.degree. C. by putting the parts array support on a heater. Then, the heated parts are each taken out of the parts array support with a pressure fitting tool b shown in FIG. 14A. Specifically, a holder (usually a plastic tube) c of the pressure fitting tool b is inserted into a threaded hole d of the part a. The pressure fitting tool b then pressure fits the part a in a part fitting hole f of a work e. The part a thus pressure fitted is hot enough to cause softening and migration of the resin of the work e around the hole f into grooves or recessed portions g, which are preliminarily formed in the outer periphery of the part a, and it is thus secured to the work e when the softened resin is solidified again. The softened resin is momentarily solidified again. Thus, even by pulling out the pressure fitting tool b from the part fitting hole f as soon as the part a is pressure fitted therein, the part a will not be pulled out together with the pressure fitting tool b but remain in the part fitting hole f.
In the prior art method of pressure fitting using a machine, a work is set on and secured to a work bench. In this state, a pressure fitting tool is caused to take hold of each of heated parts, then be moved to a position over a part fitting hole of the work and then be lowered. Each part held by the pressure fitting tool is thus pressure fitted and secured in position on a part fitting hole. The parts are thus pressure fitted one by one. Again in this case, the resin of the work around the part fitting hole with a part pressure fitted therein, is caused to soften and migrate to the part and solidified again.
The above prior art manual method had the following problems
The operation of manually setting parts one by one to form a lattice-like array on the parts array support, is very time-consuming.
It is more time-consuming and very cumbersome to take hold of each of the parts in the array on the parts array support and pressure fit the part in each part fitting hole by using the pressure fitting tool. Actually, not only an unskilled but also a skilled operator may slantedly or insufficiently pressure fit parts in part fitting holes, thus producing a rejected product. Besides, different operators will give rise to finish fluctuations even if they are all skilled. Furthermore, since a work usually has a plurality of part fitting holes, the manual operation may rise give to missed part fitting holes left without parts pressure fitted therein. The probability of missing is increased with increasing number of part fitting holes the work has. Moreover, the heating of the parts array support on the heater gives rise to the possibility of causing a burn to the operator due to careless operation.
The above prior art method using a machine had the following problems.
The pressure fitting tool for pressure fitting a part, which is moved while holding a part and is lowered and raised for the pressure fitting the part, requires provision of a part holding mechanism, a moving mechanism and a pressure fitting mechanism, thus complicating the overall mechanism. In addition, the pressure fitting tool may be brought to a deviated position form the position to pressure fit a part. Such deviation of position may result in slanted pressure fitting of a part or clogging during the pressure fitting and defective pressure fitting. Furthermore, the pressure fitting tool can pressure fit only a single kind of part in one operation cycle, i.e., one cycle sequence of movement and lowering and raising. Therefore, even by providing two or more pressure fitting tools, the operation efficiency cannot be improved because during the pressure fitting operation of one of these tools for pressure fitting a particular kind of part, the other tools can not be operated.
An object of the present invention is to provide an automatic parts pressure fitting apparatus, which can preclude the missing of part fitting holes left without pressure fitting parts therein, reduce such defective results as position deviation, insufficient pressure fitting and bending after pressure fitting, accurately and quickly pressure fit parts in part fitting holes, improve the operation efficiency, greatly reduce labor and ensure safe operation without any possibility for the operator to get burnt during operation.